This invention relates to a safe, economical process for converting sodium sludge and other dangerous wastes containing metallic sodium, lithium and potassium into products of economic value. Waste materials containing metals, such as sodium, potassium, lithium and calcium are quite hazardous because of their high chemical reactivity with water and the danger of explosive reactions. These metals react readily with ambient atmospheric moisture to liberate hydrogen gas and much heat. The reaction of sodium, for example, is sufficiently exothermic to result in ignition or explosion of the hydrogen gas and ignition of the sodium metal. Disposal of wastes containing these metals has been a problem. Small quantities are burned. Large quantities, such as the waste sodium sludge from a Down's cell, are undesirably dumped at sea. The principal metal waste in the sodium industry is the sodium sludge containing typically about 70 percent sodium, 20 percent calcium and 10 percent oxides and chlorides of sodium and calcium by weight.
It is economically attractive to react the waste metals with an aqueous solution and methods have been proposed. U.S. Pat. No. 2,527,443 describes a method for introducing sodium sludge into the lower portion of an upflowing stream of an aqueous sodium hydroxide solution. Applicant has found that this method is technically unsound and results in violent explosions as the reacting sludge rises in the vertical column. The invention has not been adopted for industrial use.
Essentially pure, solid sodium can be reacted with flowing water. British Pat. No. 574,360 describes a nozzle with a center feed of sodium in rod form which is contacted with a surrounding flow of water. This method necessitates the use of solid metals in rod form. Water flow removes the reaction heat and prevents the sodium from melting and causing an explosion. Tests conducted by applicant show that sodium sludge could not be reacted in such an apparatus even if it were in solid rod form. Its reduced thermal conductivity prevents effective heat removal by a flowing aqueous solution and melting occurs even at high liquid-solid interfacial velocities.
U.S. Pat. No. 2,660,517 describes a method of reacting liquid sodium (or sodium sludge) with wet steam. The liquid sodium is floated on a pool of molten anhydrous sodium hydroxide at 325.degree. to 700.degree. C. Steam containing 10 to 25 percent liquid water is bubbled up through the sodium hydroxide to react with the liquid sodium and form more anhydrous sodium hydroxide. It is claimed that the reaction heat is absorbed by vaporizing entrained water. The thermal regime of this process appears to be dangerously close to violent conditions. Liquid sodium will burn in water vapor. If the flow of water vapor stops, an explosion occurs (R. N. Newman, A. R. Pugh and C. A. Smith, Conference on Liquid Alkali Metals, British Nuclear Energy Society, 1973). Heat from the reaction of water vapor with liquid sodium tends to raise the sodium surface to its boiling point (883.degree. C.) where the reaction becomes even more exothermic. Explosions are associated with sodium in a dispersed state at its boiling point.
There is a definite need for a process whereby the more reactive alkali and alkaline earth metals can be converted safely and economically into their respective hydroxides. There is particular need for a method to convert waste sodium sludge and scrap sodium into economically useful hydroxide solutions and to eliminate the pollution of ocean dumping.